ES2338057T3 - CONTROL METHOD FOR AN INDUCTION KITCHEN PLATE AND INDUCTION KITCHEN PLATE ADAPTED TO CARRY OUT THAT METHOD. - Google Patents

Abstract

Method for controlling the power delivery to a pair of induction heaters/coils belonging to a household cooking hob. The method comprises a simultaneous activation of both the induction heaters at the same frequency during a first fraction of the control period, and the activation of only one induction heater at a second frequency for a second fraction of the control period.

Description

Control method for a cooktop induction and induction hob adapted to carry out Said method

The present invention relates to a method to control the power delivery to a couple of induction heaters / coils belonging to a plate domestic kitchen. Induction cookers are based on the inductive effect to heat placed kitchen containers on your kitchen surfaces. The heating of the container is produced by inductive coupling of the metal pan with the variable magnetic field with the time generated by the device.

The basic functional architecture or structure which is put into practice in an apparatus to generate the field electromagnetic, comprises at least one inductor for each zone of induction heater cooker (including a coil metal referred to, usually, as "spiral"), an electric power generator to power the coils, an electronic control unit intended for monitor the power supplied by the coils and to carry make the settings by the user, entered through the user interface.

The so-called "parasitic currents" are induce on the bottom or bottom face of the metal pan by cause of the electromagnetic field generated by the inductor coil. The electronic control unit monitors the power delivered to the coil by means of a high frequency excitation signal. The excitation signal controls the operations of a converter AC-AC (alternating current in alternating current - "alternate current-alternate current (AC-AC) ") (referred to in successive as "converter"), provided with switches solid state (insulated gate bipolar transistor -IGBT ("Insulated Gate Bipolar Transistor") -, or similar) that They provide the coils with an adequate AC current. In consequently, the coil generates, in the surrounding space, a field electromagnetic variable in time and whose amplitude and frequency determine the amount of power that is supplied to the pan. The induced currents find at the bottom of the vessel a electrical resistance R that depends mainly on the material characteristics and penetration depth of electromagnetic field (namely the skin effect). Currents induced generate heat according to the Joule effect.

It is known that some circuits generate such electromagnetic field variable in time, but, as consequence of typical operating frequencies and considering the power that is normally supplied by a single heater (ranging between 0 and 3 kW), are usually adopted Two main resonant converter circuits: the converter resonant half-bridge (HB - "Half-Bridge") (Figure 2) and the quasi-resonant converter (QR - "Quasi-Resonant") (Figure 3). The signs of excitation of these converters typically range from 20 kHz to 50 kHz

These converters, thanks to switches of solid state like IGBT, convert DC link voltage (direct current - "DC (direct current)") rectified static in a square voltage profile or waveform that is supplies a resonant circuit RLC, where L is the impedance of the coil, C is the resonant capacitor and R is the resistance of the circuit, linked to the characteristics of the pan.

In the case of the HB topology, the circuit resonant "accumulator" (the L and C of the resonant circuit) It is defined by the inductor coil L1 and the two capacitors resonants C1 and C2. An excitation signal S1, formed with a square waveform of frequency f_ {HB}, switches, directly or through a switching logic SL ("switching logic "), two IGBT's (SW1 and SW2), alternating, within the period control T, the voltage applied to the resonant circuit. The signal O_ {1} of the HB converter during the control period T, is a forced oscillator The alternating current that flows through the coil L1 induces the variable electromagnetic field over time in the surrounding area, necessary to heat the pan placed over.

In the case of the QR topology, L2 and C3 define the resonant "accumulator" circuit. The only IGBT (SW4) of circuit is excited with a square wave signal (S2) generated by electronic control, which powers the output of circuit (O2) only during the T_ {ON} portion of the excitation period and let the output of circuit (O_ {2}) during T_ {OFF}. In fact, during T_ {ON}, the  IGBT drives and the L2 coil is charged from the link voltage of Static CC, while, in the next time of period T, when the IGBT is open, the circuit is swinging freely as a damped harmonic oscillator. T_ {OFF} is defined by therefore, as the time elapsed between the end of T_ {ON} and the temporal instant in which the oscillating current flowing to through the capacitor C3, or the voltage across its terminals, go through the zero value for the first time. T_ {OFF} is therefore linked to oscillator physics with the selected T_ {ON}, of such that the free oscillation is determined by the L2, C3, R of the system (when the pan is placed on the coil), in the that the initial oscillatory conditions are defined by the coil load L2 (charge) accumulated during T_ {ON}. The power supplied by the spiral coil L2 is adjusted, by therefore, choosing the appropriate time T_ {ON}.

In other equivalent embodiments, T_ {OFF} may be destined to be the time elapsed between T_ {ON} and the temporary instant for which the voltage across the coil L2 go through the zero value for the first time.

It is noted here that the output signals of AC converters are not usually sinusoids regular. For this reason, in the following description, when mention an AC frequency, this is intended to refer at the fundamental frequency of the signal in the sense of the analysis Spectral of signals.

The fundamental operating frequency of The AC signal supplied as output by the converter comes given, therefore, by f_ {QR} = 1 / (T_ {ON} + T_ {OFF}).

For an HB converter, the characteristic of power transfer of coupled systems, which is the relationship between the power P supplied from the heater to cookware, pots, pans, casseroles or similar elements arranged on it, and the frequency f_ {HB} of the excitation signal generated by the control unit electronic, it looks like the typical way an oscillator has Forced harmonic and slightly damped.

For a QR converter, the output power P saves a direct relationship with the switching frequency f_ {QR}, once T_ {ON} has stabilized, and the related power transfer characteristic of the coupled systems represents this link. Also in this case, the system power transfer feature coupled looks like the typical form of a harmonic oscillator forced and slightly cushioned.

For both converter topologies, the factor of damped oscillator is provided by the resistance R, specific to each pan, reproduced as a mirror image in the pan through inductive coupling.

In order to avoid damage to the IGBT and to increase the efficiency of the converter (which means reduce the power dissipated during switching operations), in both converter topologies the IGBT's must be switched within the narrow temporal window in which the tension through of the IGBT's is going through zero. Sometimes, IGBT's are also protected against overcurrents or excessive currents through the application of buffer networks in parallel.

The main advantage of the QR topology, in comparison with the HB topology, lies in its lowest cost, due to the reduced number of components. The disadvantages are they find in the tight temporary switching to which the IGBT

A problem that affects the two topologies when running in pairs in order to activate simultaneously two induction heaters in an uncoordinated way and optimized, is the occurrence of a flashing light too frequent and, more generally, a breach of regulations concerning the requirements for induced emissions electromagnetically

Another problem that affects both topologies of converter is the appearance of a beating noise that can occur when two or more converters are connected to it line filter or power conduction when the signal excitation operates at different frequencies. In particular, when induction heaters / coils are activated to heat the at the same time two containers located on the plate, their converters need to be excited at the right frequencies, in order to supply the required power to the containers. Provided that these frequencies differ by less than the frequency maximum audible (around 16 kHz), the conduction filter Shared can produce a mechanical vibration. A whistling noise Audible can, therefore, annoy the user.

Some of the problems above mentioned have been undertaken and solved by implementation of specific solutions. In the following two of these would be added solutions

WO 05/043737 A2 describes a Asymmetric duty cycle control method to excite two HB converters connected to respective induction coils and that work at the same time in order to supply each of the two vessels placed on top an amount of power preset

The control method described consists of keep the frequency of the excitation signal constant so square wave (S1 in Figure 2) for each of the two HB converters and properly adjust the cycle of work of the two IGBT door signals (S1_ {A} for the Door_A1 and S1_ {B} for Door_A2 in Figure 2), which allows each coil (induction heater) to supply the preset amount of power to your placed container over. It is known that, when a work cycle is modified from its  50% value up to a lower or higher value, the voltage of r.m.s. applied to the coil is reduced, which leads to a output power lower than that obtainable for the value of 50% of the duty cycle (which is the Pmax value supplied by the system to the container placed on top).

The regulation relationship, which is the relationship Pmax / Pmin, in which Pmin is the minimum power available to the vessel through the system using the modulation of the cycle work, is less than 3: 1.

When the difference between the power that has of supplying by the two coils is too large to be accommodated solely by the modulation of the work cycle, the excitation frequencies of the two coils / stoves or burners are they are displaced from each other by at least 17 kHz.

The use of an additional control parameter (duty cycle) in the topology of the HB converter makes possible to extend the range of magnitudes or power levels of allowed output and prevents the appearance of beating noise when They run multiple heaters at the same time. For other part, the asymmetric door drive takes the converter to lower efficiency, resulting in heat dissipated during switching operation, because the buffer network required to avoid this phenomenon can be specified or particularized only for a switching duty cycle dice. Moreover, the electrical and thermal stresses exerted on The two IGBT's are distributed unevenly. Finally the PWM generation (Pulse Width Modulation - "Pulse Width Modulation ") with an asymmetric duty cycle is not a cost effective solution.

A single document is disclosed by EP 0286044 AC-AC converter circuit, either HB type or QR, which is shared to power two heaters of induction / coils, alternatively connected by means of a relay switch With this circuit configuration, they can low power levels that act on the CONNECTION-DISCONNECT modulation ("ON-OFF") when switching between the two coil elements, keeping the set power active every element for the time required to supply the power Average net required. The beating noise is intrinsically avoided exciting, alternatively, only one of the coils. Such a solution has several disadvantages.

The device may cause annoying blinking bright due to frequent changes in drained current from the supply network.

The power, according to this method, is not Delivered in a smooth way. In fact, when the modulations of CONNECTION-DISCONNECTION are too slow, the switching could be perceived by the user, especially at low power levels, because these levels are realized, in practice, supplying an amount as output relatively large power for a short time, which It could potentially damage the food being cooked. When, on the contrary, both heaters are actuated to a high power level, the user can perceive the switching between the elements, and see the boiling water and then stopping

Another way to get regulation independent of power when two converters are used  HB that work at the same frequency, consists of including, waters Above each converter, a DC Bus voltage regulator, such as a "Buck-Boost" increment (booster - "boost"), reduction (fader - "buck"), or similar, well known. This solution is commonly used in industrial applications but is almost absent in the consumer applications, due to the increase in cost, to the power dissipation and the space occupied by the additional stage Power conversion

It is, therefore, a purpose of the present invention provide a method that does not have the disadvantages of prior art More specifically, the method according to The present invention allows simultaneous operation of two induction heaters avoiding the appearance of beating noise at time that a smooth supply of the magnitudes is provided or preset power levels.

The method is then not limited by intrinsic characteristics of the converter and the set of coils, being applicable to HB and QR converter topologies and to similar topologies or those derived from them. In An additional stage, the method can be refined by selecting among the possible work modalities the one that optimizes one or more additional work parameters, such as minimizing the effect flashing light, minimizing efforts in the components, or overall efficiency.

The method can be applied using scales of slow and fast time, and prevents the appearance of noise from flicker.

Other features and advantages of this invention will be readily revealed by the following detailed description and example, when read in the light of accompanying drawings, in which:

- Figure 1 shows a sectional view and schematic of an induction cooktop;

- Figure 2 shows the circuit diagram of half bridge converter topology, known in the technique;

- Figure 3 shows the circuit diagram of quasi-resonant converter topology, known in the art;

- Figure 4 is a representation of the architecture or functional structure for a cooktop of induction according to the present invention;

- Figure 5 shows the characteristic curves of power of two heaters according to the invention;

- Figure 6 shows a graphic diagram of the power supplied by two induction heaters during a control period, when heaters are excited according with the method of the present invention;

- Figure 6A shows one of the possible embodiments of the method according to the present invention, in the shown the activation sequence of the two heaters of induction for two consecutive control periods;

- Figure 7 shows another embodiment of the method in which the control period comprises a third fraction of time;

       \ newpage
    

- Figure 8 is a diagram of a finite number of calculated solutions, represented against the work cycle in percent;

- Figure 9 is another diagram of them data shown in Figure 8, highlighting the solution chosen to optimize the light flashing parameter;

- Figure 10 shows the diagram of Figure 8, in which the chosen solutions have been highlighted;

- Figure 11 is a flow chart schematic of a possible implementation of the method according to the present invention, and

- Figure 12 is the representation of a further embodiment of the method according to the present invention.

Referring to the drawings, it provides an induction plate 10 with a ceramic surface of  glass 20 or similar, a user interface (not shown), two induction heaters / coils A, B (also known as stoves or burners) and a common control circuit 90, provided with two converters 40, 45 (this architecture also receives the configuration name of twin converters) in order to excite heaters / coils A, B in a coordinated manner. Every converter 40, 45 may be of the known type, based, either on the HB topology (shown in Figure 2) or in the QR (which is shown in Figure 3), or derived from these types.

In a different board configuration (no illustrated), more pairs of induction heaters and the control circuit is designed to excite, in a coordinated way, each pair of coils A, B. In Other plate configuration (not shown), two induction coils A, B, excited according to the present method, define a induction heater equipped with two heating zones.

Two kitchen utensils C1, C2, such as pots, pans, casseroles or the like, are placed on the plate surface 20, in correspondence with the heaters induction / coils A, B located below. The levels of power PA_ {0}, PB_ {0} to be supplied, respectively, from heater A and from B to its overlapping kitchen utensils C1 and C2, are set in the electronic control unit before starting operation, directly related to the entries received from the user to through the user interface. PA_ {0} power levels, PB_ {0} of the two heaters A, B can be adjusted, by example, in PA_ {0} = 2.5 kW and PB_ {0} = 800 kW.

The method of the present invention is a control algorithm that allows two heaters to induction / coils A, B simultaneously supply the levels of preset power PA_ {0}, PB_ {0} on average over from the control period T, to their respective kitchen utensils C1, C2 located above, to excite their individual converters in a coordinated way. The method is substantially a control of "open loop" that is based on the assumptions that characteristic power curves of the two heaters of induction A, B are known.

Generalizing the definition provided in above, the characteristic power curve is the ratio existing between a characteristic of the signal S1, S2 that excites the converter 40, 45, which consists of an excitation signal Adjustable periodic S1, S2, and PA, PB power supplied to the specific kitchen utensil C1, C2 placed on top, inside the Induction heater operating range A, B. The characteristic of the periodic excitation signal S1, S2 that has been to consider in the construction of the characteristic curves It depends on the type of converter 40, 45 that is used and can be, for example, f_ {HB} in the case of HB 40 converters, or f_ {QR}, with a certain T_ {ON} -T_ {OFF}, for  QR 45 converter types. Equivalently, they can other characteristics of the excitation signals S1, S2 be used for the construction of the characteristic power curve.

A convenient selection is then made for the control period T in order to obtain a soft heat supply. In a preferred embodiment, the period of control T is smaller than the thermal time constant Tau of the cookware placed above (C1, C2), which, Normally, it is not less than 12 seconds, in order to provide a smooth supply of power to kitchen utensils (C1, C2) placed on top. According to this, a period of control suitable can be adjusted, for example, in T = 5 seconds.

The T value can also be chosen so that be a multiple of the half-period of the supply network of power.

In the example illustrated in Figures 1 to 4, two identical induction heaters are connected with two converters The first heater A is connected to a HB 40 converter, while the second heater B is connected to a QR 45 converter. In other embodiments (no described), the two induction coils / heaters can be connected to converters belonging to the same topology, since of HB or Q or the like, or derivatives thereof. In realizations different, the power dimension of the two heaters A, B It may not be, necessarily, the same.

In order to apply the method of this invention, it is required to build, for each of the two heaters / coils A, B coupled with its cooking utensil C1, C2 placed above, its characteristic power curve specific. This operation has to be carried out when place a kitchen utensil for the first time on the surface of the plate, above the induction heater, before its activation.

In an example implementation of the method of according to the present invention, for the first heater A, the characteristic power curve PA = F_ {C1} (f_ {HB}) is creates by first establishing a correspondence relationship of the power supplied by the induction heater to C1 kitchen utensil placed above a certain number of frequencies distributed in the frequency range for the The induction system has been designed to work.

This power correspondence relationship is it achieves staggering the frequency f_ {HB} of the signal S1 which excites the power converter HB in the range of operation f_ {HB1}, f_ {HB2}, ..., f_ {HBN} and determining the associated power outputs PA_ {fHB1}, PA_ {fHB2}, ..., PA_ {fHBN} for each step 1, 2, ..., N with any of the known methods (that is, disruption resistances, etc.).

For burner B, in a similar way, the power transfer characteristic related to the kitchen utensil C2 located above, is PB = F_ {C2} (f_ {QR}, T_ {ON}) or, equivalently, PB = F_ {C2} (T_ {ON}, T_ {OFF}), and is built by staggering the T_ {ON} of the excitation signal S2 over the interval of heater operation, reading T_ {OFF} with the counter of the electronic control unit, and determining the corresponding power outputs PB_ {fQR1}, PB_ {fQR2}, ..., PB_ {fQRN}, and is calculated by control unit 90.

After the operation of establishing the correspondence relationship, it is possible to rebuild in its entirety,  when required, the characteristic power curves PA = F_ {C1 (fHB)} and PB = F_ {C2} (f_ {QR}, T_ {ON}), or PB = F_ {C2} (T_ {ON}, T_ {OFF}), related to specific kitchen utensils C1, C2 arranged above, interpolating the individual points for which a Sampling by using one of the known numerical methods, for example, the 5th order polynomial method. The curves features are then memorized in the unit memory control 90 in the form of query tables, or in the form of equation.

The characteristic curves PA = F_ {C1} (f_ {HB}) of the first heater A, and PB = F_ {C2} (f_ {QR}), or PB = F_ {C2} (T_ {ON}, T_ {OFF}) for the second heater B, are represented graphically in Figure 5.

It stands out here that, to deal with the slow variations of the power transfer curve due to changes in load impedance (as a result of pot heating, pot movement, etc.), the system you may need to continually check the consistency of your curve of stored power transfer, with the power that is actually supplies, in order to shoot or trigger a new uptake of such a curve under the evidence that it has occurred, since the last collection, a substantial deviation calculated DE. In an implementation example, the amount of DE deviation that can be tolerated before a new one is considered necessary uptake, is directly related to the desired accuracy for power control, and can preferably be adjusted in the interval between 2% and 10% relative error. Can, by therefore, set a threshold error T_ {HE} to compare the calculated deviation DE, that is, T_ {HE} = 5% relative error. When the DE deviation is greater than the threshold error T_ {HE}, the characteristic power curve P = F_ {C1} (f_ {HB}), P = F_ {C2} (f_ {QR}), or P = F_ {C2} (T_ {ON}, T_ {OFF}) is built again.

It also stands out that, in some embodiments of the present method, standard power characteristic curves related to standard kitchen utensils that are going to use on the stove, can be stored in the memory of the electronic control control unit 40 during the phase of manufacturing and, therefore, when the utensil of related kitchen, one or more of the curves are used memorized

In the event that only heating is required a single kitchen utensil C1 or C2, control 40 activates its induction heater A or B by application to the converter 40, 45 to which the heater is connected, of a signal of adequate excitation S1, S2, in order to allow the heater to induction supply to kitchen utensil C1, C2 located by above, the preset power level PA_ {0} or PB_ {0}. The characteristics of this appropriate signal S1, S2 are calculated at from the heater power characteristic curve of individual induction, previously generated, directly or by the interpolation of the points with which the correspondence relationship.

In the example illustrated in Figures 4, 5, 6, 6A, 8, 9, 10, heat the first kitchen container C1 located above the first heater A, without operating the burner B (heater B is OFF), requires exciting the HB converter with an excitation signal S1 that operates at a f_ {HBPA0} frequency = 24 kHz, while at the same time heat the second cooking vessel C2, located above the second heater B, without operating burner A, requires excitation of the QR converter with an excitation signal S2 which operates at the frequency f_ {QRB0} = 26 kHz, where T_ {ON} = 15 \ mus.

When the two kitchen utensils C1, C2 need to be heated at the same time, the method of according to the present invention. According to this method, two induction heaters A, B supply the power preset PA_ {0}, PB_ {0} on average over the period T, to their respective kitchen utensils C1, C2, by exciting the two converters with their respective periodic signals S1, S2, including a sequence in two fractions illustrated in the Figure 6A, for which:

- during a first fraction T1 of period T, the two induction heaters A and B are simultaneously activated by exciting their converters 41, 44 with a signal S1, S2 that works at the same first frequency f1, which means that f_ {QR} = f1 and f_ {HB} = f1;

- during a second fraction T2 of period T, one of the two induction heaters A, B is disconnected at stop its excitation signal S1, S2, while the other heater continues to run when your converter is excited with a signal S1, S2 that operates at a second frequency f2.

Of course, also the reverse sequence in the that T2 precedes T1 is included in the present invention, since the order of the temporal fractions T1, T2 within is not important of the control period T, but rather, that they occur.

The induction heater between the two heaters A, B to be disconnected during the second fraction T2 is one that, if it works only (with the other heater disconnected) to the magnitude or level of power required, I would need an excitation signal that had the most frequency high. According to the typical shape of the characteristic curves power, the heater to be disconnected is normally the one that has to supply the lowest power level between two identical induction heaters.

In the example described, being the first Heater A excited with an S1 signal operating at f_ {HBPA0} = 24 kHz in order to supply a power of 1.5 kW to your C1 kitchen utensil placed above, and being the second Heater B excited with an S2 signal operating at F_ {QRB0} = 26 kHz, with T_ {ON} = 15 \ mus, in order to supply a 1 kW power to your C2 cookware placed above, the heater that will be disconnected during the second fraction of the T2 control period is the second heater B.

In Figure 5, the frequencies f_ {HBPA0} = 23 kHz and F_ {QRB0} = 34 kHz, which satisfy the power levels default PA_ {0} and PB_ {0}, are represented on the respective power characteristic curves P_ {C1} = F_ {C1} (f_ {HB}) and P = F_ {C2} (f_ {QR}), or P = F_ {C2} (T_ {ON}, T_ {OFF}) relative to heaters induction A, B coupled with their respective cookware C1, C2 placed above.

In the preferred embodiment of the method of according to the present invention, T = T1 + T2, where T1 can precede T2 or vice versa. In a different method application, not described, T1 and T2 are alternated continuously in the consecutive excitation periods T, during activation of the heaters, so that T1 precedes T2 in the first control period T, while in the next period of control T, T2 precedes T1, and so on.

It could also be the case, in another embodiment of the method shown in Figure 7, in which there is also a third fraction T3 of period T, located within the same period T, that the two heaters of induction were disconnected. This is the case when required. regulate the burners at very low power levels, for that the frequency of the excitation signals S1, S2 should be too high to switch status switches solid. In such a case, a low power is supplied (on average) to kitchen utensils, by reducing the time of heater activation over the period T introducing a dead time, which is the third fraction T3. In In this case, T = T1 + T2 + T3.

In the preferred embodiment, once defined D = T1 / T, the calculation of the first frequency f1 of the S1 signals, S2 that excite the two converters of the heaters of induction A, B during the first fraction T1, and the calculation of the second frequency f2 of the signals S1, S2 that excite the single converter of one of the induction heaters during the second fraction T2 of period T, results from the resolution of the following set of equations:

PA_ {0} = PA (f_ {1}) * D + PA (f2) * (1 - D)

PB_ {0} = PA (f1) * D

A preferred way to solve the previous set of equations is to "sweep" the parameter D along a certain number n discrete steps in the range of [0, ..., 1]. A solution of the previous system of equations is then sought for each of these steps | Each solution, when it exists, is defined by a set of three values of the parameters {D = D_ {n} , f1 = f_ {1n} , f2 = | f_ {2n} }, so that each solution meets the power needs of PA_ {0} and PB_ {0} over the period T. A subset of these solutions, evenly distributed within the range, can be calculated by known algebraic methods. of supported operation. This calculation is easy to perform with a processor that is normally used for commercial applications, which requires a few moments of CPU time [central processing unit - "Central Processing Unit"].

In the example, a calculation has been carried out of a certain number of allowed solutions. The solutions calculated are plotted in Figure 8, in which the horizontal axis shows D.

Calculated solutions can be stored in the memory of the electronic control unit 90 for its Additional processing or treatment. In fact, choosing a solution among the whole set of available solutions can be done by applying one or more optimization criteria.

It is noted here that the choice to excite the two induction heaters / coils A, B together in the first fraction T1 with excitation signals S1, S2 operating at the same first frequency f1, prevents the appearance of noise acoustic noticeable by users during the operations of heating. For the second fraction T2, the problem is not presents, having only one heater running.

At an additional stage of the method, they can apply additional criteria in order to select from the supported solutions, the one that optimizes one or more parameters Working circuit. These parameters depend on the type of installation chosen for the device and are related, by example, with the minimization of power losses through of solid state switches during the operation of switching, or with the reduction of tensions or stresses in the component, or with the minimization of the flashing light when it is switched between fractions T1, T2 (and, eventually, with the third fraction T3 of period T).

As a consequence, when it is established any of the optimization criteria above mentioned, another functional relationship is defined (in the form of equation or query table) between the characteristics of the excitation signal S1, S2 and a functional parameter linked to the optimization criteria

The combination of the new restrictions defined by the functional relationships with the set of previously described equations, provides a subset of solutions that optimize the functional parameter, and, in Consequently, the criteria. It is possible to apply more than one criterion to when determining the optimized solutions f1_ {OPT} and f2_ {OPT}.

In Figure 9 they have been plotted curves that represent some examples between the criteria of optimization

Ultimately, the choice can be made end of the first frequency f1 = f1_ {OPT} and the second frequency f2 = f2_ {OPT}.

In the example, as highlighted in the Figures 9 and 10, the optimized solution f1_ {OPT}, f2_ {OPT}, D chosen is the one that satisfies in the most favorable way the criterion on the minimum light flashing. Finally, you have as a result that f1 = f1_ {OPT} = 25.8 kHz, f2 = f2_ {OPT} = 21.8 kHz, D = 43%.

It is noted then that normally the value of the first calculated frequency f1, f1OPT, is different from the value calculated for the second frequency f2, f2OPT, but that, in Some specific cases could be identical.

Once a solution has been identified adequate from among the available set, expressed in terms of the three outputs: f1, f2, D (where D1 = T1 / T), where D is a number real that goes from 0 to 1, [0, 1], it is possible to apply a further refinement of the present invention.

In practice, any implementations of the two CONNECTION / DISCONNECTION control algorithms ("ON / OFF") and PWM, apply some form of discretization or quantization of time \ Deltat, which is the quantization of T or temporal segment, to solution D, which thus becomes a rational number <D1>. For example, assuming the solution for D = 0.37 and having chosen T = 5 seconds, and choosing \ Deltat = 0.25 seconds, the closest Duty Cycle available <D1> will be equal to 0.35 (0.35 is equal to approximately (0.37 / (0.25 / 5)).

If the temporary segment \ Deltat is chosen synchronized with the power supply network and equal to the half of the period of the supply network period of power, that is, 10 mseconds, it is possible to apply signals from excitation S1, S2 that provide control patterns such as the one described in the so-called "cyclic jump" method. Saying method is well known in the art and is described in the document US 4,871,961. This document describes a method to control the power supply to electrical loads with a minimum of transient switching currents, while providing finer power control.

According to this, the method according to the present invention has to include the following steps additional, before being executed (as shown in Figure 12):

- Find the best approximation of the Cycle of Required work <D1> with the given choice of \ Deltat / T, calculating: <D1> = rounding of (D / (\ Deltat / T)), where <D1> is the discretized or quantized value of D.

- Segment the control period T according with the quantization of 10 ms.

- Change the order of the segments.

In a preferred embodiment, the permutation of the order of the segments is carried out with a first stage which consists in classifying the segments of the control period T according to their total power values (applying classification criteria according to agreement, either with a increasing value or with a decreasing value), such that the total power value for each segment is the sum of the powers supplied by the two heaters in the same segment. This classification can be done with the software, establishing a correspondence relation of the segments of the control period T, together with their total power values, in an ordered set or associated logical matrix of segments, and then classifying the matrix of segments of agreement with the selected criteria. In a second additional stage of permutation, the new sequence of segments is generated by taking one of the segments from the top of the array of classified segments and adding the segment to a new ordered matrix containing the new ordered sequence of segments, and then taking two segments from the bottom of the segment matrix, and adding the two segments to the ordered matrix. This procedure ( top-top-bottom sequence) must be repeated until all classified segments have been rearranged.

This permutation method results particularly effective in terms of compliance with regulatory requirement of low emission regulations frequency, such as flashing (IEC61000-3-3) and those related to Harmonics (IEC61000-3-2).

An equivalent reclassification method consists of a sequence of segments that is created by taking two segments from the bottom of the array of segments, followed by a segment taken from the top of the array ( bottom-bottom-top-top sequence ).

The stages of one of the possible implementations have been plotted in Figure 12. In this representation, the solutions defined D, f1 and f2, or, when the additional optimization criterion is applied, D, f1_ {OPT} and f2_ {OPT}, are indicated by the reference sign 1. The following stage is represented by the reference sign 2, in which the control period T has been segmented into \ Deltat / T control segments that have a temporary duration \ Deltat. After this operation, the segments have been swapped within of the control period T. In Figure 12 one of the possible permutations applicable in accordance with this invention, referred to with the sign 3. In this representation, the short bars correspond to the segments of time referred to the second fraction of the control period, before the segmentation operation, in which only one is activated of the burners with an excitation signal S1, S2 that has a f2 frequency. The configuration or cycle skip pattern corresponding is shown in graph 4.

The test carried out by the Applicant has shown that 21 time segments (i.e., T / \ Deltat = 21) provide a good compromise between the quantization error (this is, the degree of fractionation or granularity of the regulation) and flickering behavior (which adapts to the code until jumps 1,300 W power).

This additional refinement of the method that introduces the method of cycle jumps, allows the supply of a wide range of average power levels, which ensures a Smooth supply and flicker-free operation.

Finally, being the set of equations used in this method independent of the standard period T, the method, additional steps and other additional refinements They can be applied on slow as well as fast time scales. Therefore, cycle jump techniques are applicable.

Claims (15)

1. A method to simultaneously activate two induction heaters (A, B) of an induction hob (10) or similar, so that each induction heater (A, B) is connected to a converter (HB, QR) for independent regulation of pre-established magnitudes or power levels (PA_ {0}, PB_ {0}) to be supplied from each heater (A, B) to a superimposed kitchen utensil (C1, C2), such that the converters (HB, QR) are excited with periodic signals adjustable (S1, S2, f_ {HB}, f_ {QR}, T_ {ON}, T_ {OFF}) during a predetermined control period (T), so that the method It comprises the stages of: - simultaneously activate the heaters induction (A, B) by driving their converters (HB, QR) with adjustable periodic signals (S1, S2, f_ {HB}, f_ {QR}, T_ {ON}, T_ {OFF}) that have an identical first frequency (f1, f1_ {OPT}) during a first fraction (T1) of the period of control (T), - activate only one of the heaters induction (A, B) previously activated during the first portion (T1), by exciting its converter (HB, QR) with a signal (S1, S2, f_ {HB}, f_ {QR}, T_ {ON}, T_ {OFF}) a second frequency (f2, f2_ {OPT}) during a second fraction (T2) of the control period (T).

         \ vskip1.000000 \ baselineskip
      

2. A method according to claim 1, characterized in that it also includes the step of constructing the characteristic power curves (PA, PB) for each induction heater (A, B) coupled to its corresponding kitchen utensil (C1, C2), placed above, and why the characteristic power curves (PA, PB) are constructed and stored in the memory of the control unit before activation. 3. A method according to claim 1 and claim 2, characterized in that the control period T is smaller than the thermal time constant (Tau) of the cookware (C1, C2) located above, at in order to provide a smooth power supply to the cookware (C1, C2) placed above. 4. A method according to any of the preceding claims, characterized in that the first frequency (f1, f1_ {OPT}) is different from the second frequency (f2, f2_ {OPT}). 5. A method according to any of the preceding claims, characterized in that the induction heater (A, B) to be disconnected during the second fraction (T2) is that between the two induction heaters (A, B ) that would be excited at the highest signal frequency (F_ {HBPA0}, F_ {QRPB0}) to supply the required power level (PA_ {0}, PB_ {0}) when it activates itself. 6. A method according to any of the preceding claims, characterized in that the first frequency (f1, f1_ {OPT}), the second frequency (f2, f2_ {OPT}) and the first fraction of time (T1) are chosen Among the supported solutions that are calculated by solving the following set of equations: PA_ {0} = PA (f_ {1}) * D + PA (f2) * (1 - D) PB_ {0} = PA (f1) * D. 7. A method according to claim 6, characterized in that the first frequency (f1_ {OPT}), the second frequency (f2_ {OPT}) and the first fraction of time (T1) chosen from among the admitted solutions of the first set of equations, are those that also optimize one or more criteria selected from the group consisting of: - power uniformity between two fractions consecutive (T1, T2) of the control period (T), - overall efficiency, - minimum flashing light, - efforts in the components.

         \ vskip1.000000 \ baselineskip
      

A method according to any of the preceding claims, characterized in that the first fraction (T1) and the second fraction (T2) of the control period (T) are continuously alternated during the temporary activation of the heaters (A, B). 9. A method according to any of the preceding claims, characterized in that the power (P_, P_) supplied to the cookware (C1, C2) is measured continuously during the activation of the heaters ( A, B), and the deviation (DE) between the measured value (PA_ {0}, PB_ {0}) and the corresponding value of the power characteristic curve is calculated, and why, when the deviation (DE) is greater than a predetermined threshold error (T_ {HE}), the method includes the additional steps of: - build a new characteristic curve (PA, PB), - calculate a new first frequency (f1, f1_ {OPT}), the new second frequency (f2, f2_ {OPT}) and a new first portion of time (T1, D), - restart heater activation with the new calculated solutions (f1, f1_ {OPT}, f2, f2_ {OPT}, T1, D).

         \ vskip1.000000 \ baselineskip
      

10. A method according to claim 9, characterized in that the predetermined threshold error (T_ {HE}) is in the range between 2% and 10% of the relative error. 11. A method according to claim 6 or claim 7, characterized in that it further includes the additional steps of: - find the best approximation of the Cycle of required work (<D1>), - segment the control period (T) according with a time segment (\ Deltat), - permute the order of the segments.

         \ vskip1.000000 \ baselineskip
      

12. A method according to claim 11, characterized in that the permutation of the segments includes the steps of creating and classifying a matrix of segments, and generating a new sequence of segments starting from the matrix of classified segments. 13. A method according to claim 12, characterized in that the new sequence of segments generated starting from the matrix of classified segments is created by choosing one of the segments from the top of the matrix of classified segments and adding the segment to a new ordered matrix containing the new ordered sequence of segments, and then choosing two segments from the bottom of the segment matrix and adding the two segments to the ordered matrix. 14. A method according to claim 11, characterized in that δ is synchronized with the power supply network and has a duration equal to the half-period of the power supply network. 15. An induction plate (10) having at least two induction heaters (A, B), such that each induction heater is connected to a converter (HB, QR) for independent regulation of the magnitudes or levels of power (PA0, PB0) to be supplied from each heater (A, B) to a kitchen utensil (C1, C2) placed above, characterized in that it comprises a control unit (90) configured to carry out a method according to any of the preceding claims.